Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.98	9.465%	$42.6695	$42.67	$42.65	$42.70
Purchase #2	$118.78	10.794%	$131.6011	$131.60	$131.60	$131.60
Purchase #3	$76.68	13.243%	$86.8347	$86.83	$86.85	$86.80
Purchase #4	$29.37	7.328%	$31.5222	$31.52	$31.50	$31.50
Purchase #5	$173.67	3.811%	$180.2886	$180.29	$180.30	$180.30
Purchase #6	$43.50	5.734%	$45.9943	$45.99	$46.00	$46.00
Purchase #7	$32.38	10.752%	$35.8615	$35.86	$35.85	$35.90
7 purchase totals =	$513.36		$554.7719	$554.76	$554.75	$554.80